math
posted by zack .
a group of 9 people spent $78 to go to the movies.adult tickets cost$10 each and student tickets cost $8 each.How many adult tickets were purchased?

Let x = adult tickets and y = student ones.
x = 9  y
10x + 8y = 78
Substitute 9y for x in second equation and solve for y. Insert that value into the first equation and solve for x. Check by inserting both values into the second equation. 
6 Student tickets X $8.00 = $48.00
$78.00 minus the $48.00 = $30.00
$30.00 divided by $10.00 Adult Cost = 3 adult tickets. 
3 adult tickets